When the first shots were fired at Borderline Bar & Grill, David Anderson immediately knew he was in the middle of a mass shooting. He had lived through one last year.

Anderson survived the attack at a country music festival in Las Vegas in October 2017 that left 58 people dead. On Wednesday, he again survived a gunman indiscriminately firing at people enjoying country music, this time at college night at a well-loved bar. Twelve people were killed.

“Vegas Strong” shirts were often spotted at the bar. Patrons gathered here for healing and community. The were a “family,” as Anderson described it.

Now, 13 months later, many again fled the gunshots and chaos of a mass shooting, with memories of the first terrifying experience guiding their actions in another scene of carnage.

Susan Orfanos said in a television interview that her son, Telemachus, was killed at Borderline after surviving Las Vegas.

“My son was in Las Vegas with a lot of his friends, and he came home. He didn’t come home last night,” she said. “I don’t want prayers; I don’t want thoughts; I want gun control, and I hope to God nobody else sends me any more prayers. I want gun control. No more guns.”

Telemachus Orfanos, 27, lived with his parents in Thousand Oaks and worked at a local Infiniti dealership. He was a veteran of the Navy.

“It’s a cruel thing to survive the worst mass shooting in the country in modern times, and then to be killed in another just a little more than a year later,” his father, Marc, said in an interview with The Post. “It defies logic.”

His son suffered PTSD from the shooting and had been in therapy, Marc Orfanos said.

“He felt fortunate, but also horrified at what he had seen,” he said.

In Las Vegas, Telemachus Orfanos not only survived the massacre – but helped paramedics pull those who’d been injured by gunfire from danger.

“Tel easily saved hundreds of lives,” said Brendan Hoolihan, 21, who met Orfanos for the first time amid the mayhem at the Route 91 concert. The two young men were strangers that night who quickly became teammates, rescuing people from the field beneath Mandalay Bay and later assisting victims inside the Tropicana resort.